As a simple packaging method of the optical sensor, a chip scale package (CSP) structure is proposed.
FIG. 1 is a view showing a basic structure of the CSP structure.
In the CSP structure 1, a seal glass (cover glass) 3 is arranged as a sealing member for protecting an upper portion of a light receiving unit 21 in a front surface of an optical sensor (sensor chip) 2.
In the CSP structure 1, the seal glass 3 is arranged through a resin 4 which is disposed at a peripheral portion excluding the light receiving unit 21 of the optical sensor 2. Therefore, a gap 5 is formed between the light receiving unit 21 of the optical sensor 2 and an opposite surface 31 of the seal glass 3 facing the light receiving surface 21 in the CSP structure.
In the CSP structure, wiring by wire bonding is eliminated by forming an electrode 6 by a through via hole (Through Silicon Via: TSV) piercing through the sensor chip from the front surface to a rear surface, therefore, the glass can be bonded in a wafer state in a clean room.
Accordingly, miniaturization, low costs and a dustless process can be expected as compared with a related-art COB (Chip On Board) type package.
However, the chip is formed thin in thickness as the through via hole (TSV) is formed in the CSP structure, therefore, there is a danger that chip warpage occurs due to thermal stress when a thermal process such as reflow is performed in the case where the gap 5 exists between the cover glass and the chip (optical chip) as described above.
As a method of solving the above, a CSP structure 1A in which the gap 5 is filled with the resin 4 as shown in FIG. 2 to eliminate the gap is proposed.
Hereinafter, the CSP structure not having the gap is also referred to as a cavity-less CSP structure.
When applying the cavity-less CSP structure not having the gap, the thermal stress generated in the gap of the CSP structure having the gap can be drastically reduced, thereby suppressing occurrence of warpage.
Also from an optical point of view, reflection occurring at a boundary of the gap (refractive index 1) can be suppressed by the resin having a refractive index of approximately 1.5 in the cavity-less CSP structure, therefore, increase of the light receiving amount in the optical sensor 2 can be expected.
The technique concerning the cavity-less structure is disclosed in, for example, JP-A-2007-73958 (Patent Document 1). In Patent Document 1, a manufacturing method for realizing the cavity-less CSP structure is mentioned.